1. Field of the Invention
This invention relates to a clutch control for a mechanical supercharger provided in the intake passage of the engine and driven by the output shaft of the engine through the clutch.
2. Description of the Prior Art
Recently, in engines for automotive vehicles, superchargers have been equipped to increase intake efficiency in order to increase engine output. As the supercharger, the turbo charger which is driven by exhaust gases and the mechanical supercharger which is driven by the engine output shaft are generally well known.
In the, case in which the mechanical supercharger is employed, a clutch is provided between the engine output shaft and the mechanical supercharger. By connecting or disconnecting the clutch based on the engine load, the mechanical supercharger is actuated in the high engine load region so as to increase the intake air amount and is stopped in the low engine load region to reduce driving loss. Further, in the low engine load region, the valve provided in the bypass passage which bypasses the mechanical supercharger is opened so that intake air is introduced through the bypass passage into the engine cylinder.
However, when the clutch of the mechanical supercharger is controlled in the manner described above, if the clutch is engaged at the timing the engine operating condition shifts to high engine load region from low engine load region, the mechanical supercharger has to be accelerated abruptly from zero speed to a high speed (for example 1.5 times the engine speed). This produces a large load on the engine output shaft and results in temporary reduction of engine output and shock to the power train. Further, when the clutch is engaged, the frictional elements of the clutch are kept in the condition where they are strongly pressed against each other and slide with a large mutual speed difference. Therefore, the frictional elements of the clutch wear earlier than expected.
With respect to such a problem, for example, Japanese Utility Model Application 62-12733 discloses a system which controls the clutch to engage intermittently when the engine operational condition changes to the region where the mechanical supercharger is to be actuated from the region where the mechanical supercharger is to be stopped. In accordance with this system, some reduction of shock may be expected, since the supercharger is accelerated step-wise.
However, even in the system described in the above prior art, when the clutch is engaged, especially at the first engagement stage, a large amount of shock still acts abruptly on the engine output shaft.
Also, the frictional elements of the clutch are still strongly engaged while a large amount of mutual slipping is occurring, and this engagement is repeated several times.
The engagement shock will be especially perceptible if it occurs while the vehicle is coasting and thus it will adversely affect the comfort of the driver and other passengers. Also when the vehicle is driven on high ground in a low ambient air pressure when the engine is not fully warmed up, or when the vehicle is running uphill, the engine power is reduced below its normal value. In such a condition, clutch engagement shock will greatly reduce driving comfort.
In order to prevent these kinds of problems, it is desirable to engage the clutch slowly with a smaller engagement force. But, this would result in a decreased acceleration response.
For the foregoing reasons, an object of the present invention is to suppress shock during the clutch engagement and to improve the acceleration response by controlling the slipping condition of the clutch of the mechanical supercharger when the mechanical supercharger is connected. In one embodiment, the slipping condition of the clutch is controlled in accordance with the stage of shifting of the automatic transmission. In another embodiment, the slipping condition of the clutch is controlled in accordance with the engine speed. In yet another embodiment, the slipping condition of the clutch is controlled in accordance with engine drivability.
The purpose of the present invention can be accomplished accordance with a first embodiment of the present invention by providing an engine equipped with the mechanical supercharger provided in the intake passage and driven through the clutch in response to engine condition, in which the engine has a power plant with a transmission, gear stage detecting means for detecting the gear stage of the transmission, and control means for controlling the slipping condition of the clutch in response to the gear stage of the transmission so that an engagement force of the clutch during the slipping condition becomes stronger as the gear stage becomes lower when the clutch in engaged.
In addition, the purpose of the present invention can be accomplished in accordance with a second embodiment of the present invention by providing, instead of the control means of the first inventive features, control means for controlling the slipping condition of the clutch in response to the gear stage of the transmission so that the slipping time of period becomes shorter as the gear stage becomes lower when the clutch is engaged.
Furthermore, the purpose of the present invention can be accomplished in accordance with a third embodiment of the present invention by providing, instead of the control means of the first invention features, control means for controlling the slipping condition of the clutch in response to the gear stage of the transmission so that the engagement force of the clutch during the slipping condition becomes stronger as the gear stage becomes lower and the period of slipping time becomes shorter as the gear stage becomes lower when the clutch is engaged.
In accordance with above constructions, in any of the first to the third embodiments, when the mechanical supercharger is actuated, the mechanical supercharger is connected with the output shaft of the engine through the controlled slipping engagement of the clutch. The mechanical supercharger can be accelerated moderately from stopped condition to a predetermined higher speed condition without causing a large abrupt load on the engine output shaft, whereby the shock during the clutch engagement can be reduced especially in the vehicle coasting condition in the higher gear stage.
In the first embodiment, the slipping condition of the clutch is adequately controlled in response to the gear stage of the transmission so that the engagement force of the clutch during the slipping condition becomes stronger as the gear stage of the transmission becomes lower. When the transmission is operated in the lower gear stage, transmitted torque amount of the clutch during the slipping condition becomes greater, whereby the supercharger produces sufficient supercharging effect to provide a sufficient acceleration response.
In the second embodiment, the slipping condition of the clutch is adequately controlled in response to the gear stage of the transmission so that the slipping time becomes shorter as the gear stage of the transmission becomes lower. When the transmission is operated in a lower gear stage, the clutch can complete the engagement in a short time, whereby the supercharger produces sufficient supercharging effect quickly to provide a sufficient acceleration response.
In the third embodiment, the slipping condition of the clutch is adequately controlled in response to the gear stage of the transmission so that the engagement force of the clutch during the slipping condition becomes stronger as the gear state of the transmission becomes lower and the period of slippage becomes shorter as the gear stage of the transmission becomes lower. When the transmission is operated in the lower gear stage, not only the effect of the first embodiment but also the effect of the second embodiment can be obtained.
The purpose of the present invention can also be accomplished in accordance with a fourth embodiment of the present invention by providing, in the engine equipped with the mechanical supercharger provided in the intake passage and driven through the clutch in response to engine operational condition, engine speed detecting means for detecting engine revolution speed and control means for controlling the slipping condition of the clutch when the clutch is engaged.
In addition, the purpose of the present invention can be accomplished in accordance with a fifth embodiment of the present invention by providing, instead of the control means of the fourth embodiment, control means for controlling the clutch so as to engage strongly as the engine speed increases during slipping engagement.
Furthermore, the purpose of the present invention can be accomplished in accordance with a sixth embodiment of the present invention by providing, instead of the control means of the fourth embodiment, control means for controlling the clutch so as to engage longer in time as the engine speed increases during slipping engagement.
Moreover, the purpose of the present invention can be accomplished in accordance with a seventh embodiment of the present invention by providing, instead of the control means of the fourth embodiment, control means for controlling the clutch so as to engage more strongly and for a longer time as the engine speed increases during slipping engagement.
In accordance with above constructions, in any of the fourth to the seventh embodiments, when the mechanical supercharger is actuated, the mechanical supercharger is connected with the output shaft of the engine through the controlled slipping engagement of the clutch. The mechanical supercharger can be accelerated moderately from the stopped condition to a predetermined higher speed condition without causing a large abrupt load on the engine output shaft, so that the shock during the clutch engagement can be reduced. Also, since the engine force between the frictional elements of the clutch is precisely controlled, substantial clutch wear can be prevented.
In the fourth embodiment, the slipping condition of the clutch is adequately controlled in response to engine speed. In the fifth embodiment, the slipping condition of the clutch is controlled so that the engagement force becomes larger as the engine speed increases. Therefore, the clutch shock during engagement can be effectively reduced and also clutch durability can be increased. Furthermore, when the mechanical supercharger is actuated in the high engine speed region, the mechanical super from taking a long time to reach the predetermined speed.
In the sixth embodiment, when the clutch in engaged, the clutch is engaged for a longer time as engine speed increases. Therefore, unnecessary continuation of slipping engagement in the low engine speed region can be prevented.
In the seventh embodiment, since the clutch is engaged more strongly and for a longer time as the engine speed increases, not only the effect of the fifth embodiment but also the effect of the sixth embodiment can be obtained.
The purpose of the present invention can also be accomplished in accordance with an embodiment of the present invention by providing the engine equipped with the mechanical supercharger provided in the intake passage and driven through the clutch in response to engine operational condition, lower drivability condition detecting means for detecting a condition where the power of the vehicle is lower than the normal value, and control means for controlling the slipping condition of the clutch when the clutch is engaged so that the engagement force becomes smaller in response to the signal detected by the lower drivability condition detecting means.
In accordance with the eight embodiment, when the mechanical supercharger is actuated, the mechanical supercharger is connected with the output shaft of the engine through the controlled slipping engagement of the clutch. The mechanical supercharger can be accelerated moderately from a stopped condition to a predetermined higher speed condition without causing a large abrupt load on the engine output shaft, and thus the shock during the clutch engagement can be reduced. Also, since the engaging force between the frictional elements of the clutch is precisely controlled, clutch wear is minimized. When the vehicle is running in places at high altitude where the engine power is reduced due to the low ambient air pressure, the engagement force of the clutch during the slipping condition is made smaller so as to prevent the driving feeling of the vehicle from being destroyed.